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Earthquake Scales
Richter Scale
The Richter magnitude scale is used to express the level of seismic energy released by an earthquake. Developed in 1935 by Charles F Richter he showed that the more energy an earthquake released the greater the amplitude of the wave detected by a seismograph at a given distance. In other words the size of the peak on the graph along with the distance from the epicentre gives a magnitude reading for the earthquake which will be the same from any location that is able to detect the earthquake.
The Richter scale is logarithmic so each increase of 1 magnitude is actually an increase of ten times the measured amplitude. The scale is limitless but the highest magnitude so far recorded was 9.5 for the Chilean quake of 1960.
| Intensity Scale | Description | Effects |
|---|---|---|
| less than 2 | Micro | not felt |
| 2-3 | Very Minor | not felt but recorded |
| 3-4 | Minor | often felt, no damage |
| 4-5 | Light | shaking observed |
| 5-6 | Moderate | Some damage |
| 6-7 | Strong | damaging over a 100 mile area |
| 7-8 | Major | serious damage over wider area |
| greater than 8 | Great | Serious damage over several hundred miles |
Modified Mercalli Intensity Scale
A scale developed as a way of measuring the actual effects or intensity of an earthquake at a particular location, and is expressed in roman numerals from I the weakest to XII the strongest.
The intensity scale differs from the Richter scale because the effects of an earthquake depend on location from the epicentre and local geological conditions. Whereas the Richter scale is the measurement of the magnitude of an earthquake independent of location.
| Intensity Scale |
Classification | Effect description |
|---|---|---|
| I | Instrumental | Detected only by seismographs |
| II | Feeble | Noticed by sensitive people |
| III | Slight | Similar to a passing lorry |
| IV | Moderate | Loose objects are rocked |
| V | Rather strong | Felt generally |
| VI | Strong | Trees sway, loose objects fall |
| VII | Very strong | Walls crack |
| VIII | Destructive | Chimneys fall; masonry cracks |
| IX | Ruinous | Houses collapse where ground starts to crack |
| X | Disastrous | Ground badly cracked; buildings destroyed |
| XI | Very disastrous | Bridges and most buildings destroyed; landslides |
| XII | Catastrophic | Ground moves in waves; total destruction |
Thanks to a couple of pub quiz users who pointed out errors on this page